Makoto

Low-Key ToolBar makes the block editor toolbar less noticeable and improve block editor UX.
I think block editor toolbar is useful, but too big and too conspicuous and disturbing. 
Sure, top toolbar mode is not disturbing, but is not user-friendly.
This plugin add its own setting sidebar to block editor and You can control scale, opacity, vertical position of the block editor toolbar.
By adjusting these properteis, the toolbar will be less noticeable, and it will improve UX.

Low-Key ToolBar

This plugin makes the block editor toolbar less noticeable and improve block editor UX. You can control Scale, Opacity, Vertical Position of the block …

Scott Kingsley Clark

Pretty easy setup.. just install and activate it on the site of your choice (or network activate) and set up the settings however you’d like.
This plugin supports both Per-Site and Per-Network (WordPress Multisite) settings, so you can fine tune your options based on your needs.
Other plugins you might be interested in:
<ul>
<li>Showing the Admin Bar in more cases – <a href="https://wordpress.org/plugins/always-show-admin-bar/" rel="ugc">Always Show Admin Bar plugin</a></li>
<li>Showing the Admin Bar to logged out users – <a href="https://wordpress.org/plugins/logged-out-admin-bar/" rel="ugc">Logged Out Admin Bar plugin</a></li>
<li>Customizing the Admin area based on role – <a href="https://wordpress.org/plugins/adminimize/" rel="ugc">Adminimize</a></li>
</ul>

Admin Bar Disabler

Pretty easy setup.. just install and activate it on the site of your choice (or network activate) and set up the settings however you'd like.

Low-Key ToolBar vs Admin Bar Disabler